The objectives of this application are first, to seek fundamental information about the mechanical characteristics and neuro-mechanical interactions of the respiratory muscle and second, to develop a clear analysis of the compensatory mechanisms by which patients with respiratory disease deal with the chemical and mechanical stresses associated with their disease, and of the eventual failure of these compensations. Specific aims are to identify manifestations of neural coupling between the diaphragm and rib cage inspiratory muscles, provide a quantitative analysis of EMG characteristics of respiratory muscles and their patterns of activation during voluntary respiratory maneuvers and spontaneous breathing, and to identify respiratory muscle mechanisms used by patients with chronic respiratory disease during hypoxemia, and during pursed lip breathing and their effects on respiratory gas exchange. Two related groups of experiments will be done. The first will develop a comprehensive analysis of respiratory muscle EMG characteristics during voluntary contraction in normal man, (including the effects of strength of contraction and chest wall geometry, and of the distribution of respiratory muscle activity during spontaneous breathing compared with voluntary respiratory efforts. Effects of chemical and mechanical stresses on abdominothoracic mechanics and the coordination of respiratory muscle activity will be defined. The second will describe and analyze the strategies of respiratory muscle coordinated behavior used by patients with chronic respiratory disease during rehabilitation training, and when possible, during acute episodes of respiratory insufficiency requiring hospitalization. This project is complementary to another project which focuses in normal humans on the description of one hitherto undescribed group of respiratory muscles, (the levator costae); and in patients, on the evolution of the early stages of respiratory decompensation brought about by the acute imposition of mechanical loads.